It is often necessary to measure the thickness of semiconductor substrates. For example, manufacturers of semiconductor substrates typically measure substrate thickness at various steps during the manufacturing process to ensure that the finished substrates meet industry and/or customer specifications. Similarly, the thickness of a semiconductor substrate is often measured during substrate manufacturing and subsequent integrated circuit fabrication to characterize prior processing steps that either increase or decrease the thickness of the substrate. Although there are several existing methods for measuring substrate thickness, none provide the combination of flexibility, accuracy, throughput and affordability that are demanded by the highly competitive electronics industry.
For example, one device for measuring substrate thickness is the capacitance thickness gauge. A capacitance thickness gauge typically uses a probe spaced adjacent a reference platform. When a semiconductor substrate is placed on the platform, the capacitance measured across the air gap between the substrate and probe indicates the thickness of the air gap. This thickness is subtracted from the known distance between the platform and probe to obtain the thickness of the substrate. However, the measurement of capacitance (and therefore thickness) is sensitive to the electrical properties of the substrate. Thus, to ensure accurate measurements, the capacitance thickness gauge may require frequent recalibration and/or the substrates may require additional processing to stabilize the electrical properties of the substrate. In either case, the additional time and/or expense incurred increase the costs of the manufacturing process.
Optical devices are also available for measuring substrates. However, these devices are sensitive to variations in the surface finish of substrates. As a result, the devices typically must be recalibrated repeatedly to accommodate for the varying surface finishes that occur at different points in the manufacturing process. Alternatively, multiple optical measurement devices must be provided so that a dedicated device may be calibrated for use at each measurement step in the manufacturing process.
Therefore, it would be desirable to have a system capable of quickly, accurately, and inexpensively measuring the thicknesses of semiconductor substrates regardless of the surface finish or electrical properties of the substrates.